1. Field of the Invention
The present invention relates to an interface control circuit which is utilized in the interface between logic systems for communication handshaking.
2. Brief Description of the Relevant Art
FIG. 1 illustrates an interface control circuit of the prior art. The input of buffer A is grounded. Therefore, if a "1" is applied to the "ENABLE" line of the buffer, a "0" appears at the output thereof. A problem arises, however, when the output of the buffer is to be raised to a HIGH from a LOW. If the ENABLE line of the buffer changes from "1" to "0", the voltage level of the buffer output cannot shift to HIGH instantly. Instead, Vcc potential source begins to charge line capacitance Cs through a pull-up resistor R1. As shown in FIG. 2, the rise time from t1 when the output is 10% of Vcc voltage to t2 when the output is 90% of Vcc voltage takes about 3R1Cs. In the usual situation, R1 is likely to be about 3.3K ohms and Cs approximately 50 pf, which makes the rise time 3*3.3*10.sup.3 *500*10.sup.-12, or about 500 nanoseconds. Thus, when the circuit is used in communication interfaces, the logic circuit on one side has to wait a rather lengthy time, while the other side has already finished a task and signals the status by changing the control line from LOW to HIGH. It therefore lowers the overall speed and efficiency of a digital system.